Variable and reversible resistive element, non-volatile memory device and methods for operating and manufacturing the non-volatile memory device

ABSTRACT

A variable and reversible resistive element includes a transition metal oxide layer, a bottom electrode and at least one conductive plug module. The bottom electrode is disposed under the transition metal oxide layer. The conductive plug module is disposed on the transition metal oxide layer. The conductive plug module includes a metal plug and a barrier layer. The conductive plug is electrically connected with the transition metal oxide layer. The barrier layer surrounds the metal plug, wherein the transition metal oxide layer is made by reacting a portion of a dielectric layer being directly below the metal plug and a portion of the barrier layer contacting the portion of the dielectric layer, wherein the dielectric layer is formed on the bottom electrode. Moreover, a non-volatile memory device and methods for operating and manufacturing the same is disclosed in specification.

BACKGROUND

1. Technical Field

The present disclosure relates to semiconductors More particularly, thepresent disclosure relates to semiconductor memory devices.

2. Description of Related Art

The development of semiconductor memory devices having higherintegration and lower power consumption has been the focus of recentresearch.

Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, iscomputer memory that can retain the stored information even when notpowered. Examples of non-volatile memory include read-only memory, flashmemory, most types of magnetic computer storage devices (e.g. harddisks, floppy disk drives, and magnetic tape), optical disc drives, andearly computer storage methods such as paper tape and punch cards.

Urgent demands on finding new solutions for next generation NVM havespurred many research activities in ReRAM (resistance-changerandom-access memory) studies. The promising results shown in recentReRAM works suggest that it might be able to substitute floating gatememories and become the next mainstream NVM device. The switchingresistor in the 1T+1R ReRAM cell (one transistor+1 Resistor) is realizedby backend process with a metal-dielectric-metal structure.

SUMMARY

The following presents a simplified summary of the disclosure in orderto provide a basic understanding to the reader. This summary is not anextensive overview of the disclosure and it does not identifykey/critical elements of the present invention or delineate the scope ofthe present invention. Its sole purpose is to present some conceptsdisclosed herein in a simplified form as a prelude to the more detaileddescription that is presented later.

In one aspect, the present disclosure is directed to a variable andreversible resistive element.

According to one embodiment of the present invention, the variable andreversible resistive element comprises a transition metal oxide layerfor resistance change, a bottom electrode and at least one conductiveplug module. The bottom electrode is disposed under the transition metaloxide layer. The conductive plug module is disposed on the transitionmetal oxide layer. The conductive plug module comprises a metal plug anda barrier layer. The metal plug is vertically over the bottom electrode.The barrier layer surrounds the metal plug and electrically connectedwith the transition metal oxide layer, wherein the transition metaloxide layer is made by reacting a portion of a dielectric layer beingdirectly below the metal plug and a portion of the barrier layertouching the portion of the dielectric layer, wherein the dielectriclayer is formed on the bottom electrode.

In another aspect, the present disclosure is directed to a non-volatilememory device.

According to one embodiment of the present invention, the non-volatilememory device comprises a transistor and a variable and reversibleresistive element. The transistor comprises a gate electrode, a gatedielectric layer, a first source/drain and a second source/drain. Thegate dielectric layer is disposed on a well, and the gate electrode isdisposed on the gate dielectric layer. The first source/drain and thesecond source/drain are formed in the well and are disposed at opposingsides of the gate electrode. The variable and reversible resistiveelement comprises a transition metal oxide layer, a dielectric layer andat least one conductive plug module. The transition metal oxide layer iscapable of resistance change. The dielectric layer is formed on thefirst source/drain. The conductive plug module is disposed on thetransition metal oxide layer. The conductive plug module comprises ametal plug and a barrier layer. The metal plug is vertically disposedover the first source/drain. The barrier layer surrounds the metal plugand is electrically connected with the transition metal oxide layer. Inthe formation process of the non-volatile memory device, the transitionmetal oxide layer is made by reacting a portion of a dielectric layerbeing directly below the metal plug with a portion of the barrier layertouching the portion of the dielectric layer, and thereby a remainingportion of the dielectric layer remains on the first source/drain afterthe transition metal oxide layer is formed.

In another aspect, the present disclosure is directed to a method foroperating the above non-volatile memory device.

According to one embodiment of the present invention, the method foroperating the above non-volatile memory device comprises steps asfollows. A first read voltage is applied between the gate electrode andthe well for turning on a channel between the first source/drain and thesecond source/drain in the well, and a second read voltage is appliedbetween the metal plug and the second source/drain for generatingelectric current flowing through the channel and the transition metaloxide layer. Then, the amperage of the electric current is measured, andwhether resistance of the transition metal oxide layer is set or resetis decided according to the amperage of the electric current.

In another aspect, the present disclosure is directed to a method formanufacturing a non-volatile memory device.

According to one embodiment of the present invention, the method formanufacturing a non-volatile memory device comprises steps as follows.First, a transistor that comprises a gate electrode and a firstsource/drain and a second source/drain is formed, where the firstsource/drain and the second source/drain are disposed at opposing sidesof the gate electrode. Then, a dielectric layer is formed on the firstsource/drain, and an interlayer insulating layer is formed on thedielectric layer. Then, at least one opening is formed through theinterlayer insulating layer to the dielectric layer by etching process.Then, a barrier layer on an inner wall of the opening and on a portionof the dielectric layer is formed for reacting a portion of the barrierlayer with the portion of the dielectric layer contacting the portion ofthe barrier layer to form a transition metal oxide layer, thereby aremaining portion of the dielectric layer remains on the firstsource/drain after the transition metal oxide layer is formed. Moreover,a metal plug is formed in the opening after the barrier layer is formed,and thereby the metal plug is electrically connected to the transitionmetal oxide layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present description will be better understood from the followingdetailed description read in light of the accompanying drawings,wherein:

FIG. 1A is a cross-sectional view showing a variable and reversibleresistive element according to one embodiment of the present invention;

FIG. 1B is a cross-sectional view showing a variable and reversibleresistive element according to another embodiment of the presentinvention;

FIG. 2A is a cross-sectional view showing a non-volatile memory deviceaccording to another embodiment of the present invention;

FIG. 2B is a cross-sectional view showing a non-volatile memory deviceaccording to another embodiment of the present invention;

FIG. 3 is a graph depicting the state of the non-volatile memory deviceof FIGS. 2A; and

FIG. 4A, FIG. 4B, FIG. 4C and FIG. 4D illustrate various process stepsfor manufacturing a non-volatile memory device having a transition metaloxide layer according to another embodiment of the present invention.

DETAILED DESCRIPTION

The detailed description provided below in connection with the appendeddrawings is intended as a description of the present examples and is notintended to represent the only forms in which the present example may beconstructed or utilized. The description sets forth the functions of theexample and the sequence of steps for constructing and operating theexample. However, the same or equivalent functions and sequences may beaccomplished by different examples. Wherever possible, the samereference numerals are used in the drawings and the description to referto the same or like parts.

Please refer to FIG. 1A. FIG. 1A is a cross-sectional view showing avariable and reversible resistive element 100 according to an embodimentof the present invention. The variable and reversible resistive element100 comprises a transition metal oxide layer 110, a bottom electrode 120and at least one conductive plug module 130. Transition metal oxidematerials comprise a class of materials that contain transition elementsand oxygen. They include insulators as well as (poor) metals. Often thesame material may display both types of transport properties. Thetransition metal oxide may be at least one selected from the groupconsisting of CeO₂, VO₂, V₂O₅, Nb₂, Ta₂O₅, ZnO, TiO₂, TiON, Nb₂O₅, ZrO₂,HfO, WO, CoO, NbO or NiO etc. The transition metal oxide layer 110 iscapable of resistance change. The bottom electrode 120 is disposed underthe transition metal oxide layer 110. The conductive plug module 130 isdisposed on the transition metal oxide layer 110.

The conductive plug module 130 comprises a metal plug 132 and a barrierlayer 134. The stacked metal plug 132 and the barrier layer 134 arevertically disposed over the bottom electrode 120 and electricallyconnected with the transition metal oxide layer 110. The barrier layer134 surrounds the metal plug 132. In the formation process of thevariable and reversible resistive element 100, the transition metaloxide layer 110 formed at the regions 140 and 142 is made by reacting aportion of a dielectric layer 150 being directly below the metal plug132 at the region 140 with a portion of the barrier layer 134 touchingthe portion of the dielectric layer 150 at the region 142, where thedielectric layer 150 is formed on the bottom electrode 120, and therebya remaining portion of the dielectric layer 150 remains on the bottomelectrode 120 after the transition metal oxide layer 110 is formed.

The transition metal oxide layer 110 is formed on the remaining portionof the dielectric layer 150, and the transition metal oxide layer 110 iselectrically coupled with the bottom electrode 120 via the remainingportion of the dielectric layer 150.

The dielectric layer 150 consists essentially of oxide or oxynitridematerial, wherein the oxide or oxynitride material may be selected fromthe group consisting of SiOx, SixNy, SiOxNy and combinations thereof Forexample, the dielectric layer 150 comprises one or more layers of SiOx,SiOxNy, or the like.

In the fabrication of integrated circuit devices, silicidation processesare often used in order to obtain higher circuit performance. Insilicidation, a refractory metal layer is deposited and then annealed.The underlying silicon reacts with the refractory metal layer to producea silicide overlying the gate electrode and source and drain regions.The silicided gate and source/drain regions have lower resistance thannon-silicided regions, especially in smaller geometries, and hence,higher circuit performance.

It may be desired to perform silicidation on one part of a wafer whileprotecting another portion of the wafer from silicidation. A resistprotective oxide layer a self aligned silicide block layer is depositedover semiconductor device structures and then selectively removed wheresilicidation is desired. The dedicated layer will prevent silicidationwhere it remains over the semiconductor device structures.

In one embodiment of the present invention, the resistive protectionoxide layer or a self-aligned silicide block layer in normalsemiconductor processing can be used and implemented as the dielectriclayer 150.

The barrier layer 134 is a thin layer (usually micrometers thick) ofmetal usually placed between two other metals/electrode. It is done toact as a “barrier” to protect either one of the metals/electrode fromcorrupting the other. In one embodiment, the barrier layer 134 comprisesbarrier material, wherein the barrier material may be selected from thegroup consisting of titanium nitride, tantalum nitride, indium oxide,copper silicide, tungsten nitride and combinations thereof. For example,the barrier layer 134 comprises one or more layers of titanium nitride,tantalum nitride, or the like.

The metal plug 132 is made of a metal that may be tungsten, copper,nickel, aluminum, and combinations thereof, or the like.

The bottom electrode 120 essentially consists of an impurity-dopedregion within or upon a semiconductor substrate. In the embodiment, thebottom electrode 120 may be a source/a drain or a poly gate of atransistor.

Please refer to FIG. 1B. FIG. 1B is a cross-sectional view showing avariable and reversible resistive element 200 according to anotherembodiment of the present invention. The variable and reversibleresistive element 200 is essentially the same as the variable andreversible resistive element 100, except that the transition metal oxidelayer 110 is formed on the bottom electrode 120, and thereby theremaining portion of the dielectric layer 150 surrounds transition metaloxide layer 110. In the formation process of the variable and reversibleresistive element 200, the portion of the dielectric layer 150 betweenthe metal plug 132 and the bottom electrode 120 is combined with theportion of the barrier layer 134 to form the transition metal oxidelayer 110 contacting the bottom electrode 120.

Please refer to FIG. 2A. FIG. 2A is a cross-sectional view showing anon-volatile memory device 300 according to another embodiment of thepresent invention. The non-volatile memory device 300 comprises atransistor 310 and a variable and reversible resistive element 320. Thetransistor 310 is connected with the variable and reversible resistiveelement 320.

The transistor 310 comprises a gate electrode 312, a gate dielectriclayer 313, a first source/drain 314 and a second source/drain 316. Thegate dielectric layer 313 is disposed on a well or substrate 318) andthe gate electrode 312 is disposed on the gate dielectric layer 313. Forexample, the first source/drain 314 is the source of the transistor 310,and the second source/drain 316 is the drain of the transistor 310;alternatively, the first source/drain 314 is the drain of the transistor310, and the second source/drain 316 is the source of the transistor310. In addition, the transistor 310 may comprise spacers 319. Thespacers 319 are formed alongside the gate electrode 312.

The variable and reversible resistive element 320 comprises a transitionmetal oxide layer 110, a dielectric layer 150 and at least oneconductive plug module 130. The transition metal oxide layer 110 iscapable of resistance change. The dielectric layer 150 is formed on thefirst source/drain 314. The conductive plug module 130 is disposed onthe transition metal oxide layer 110.

The conductive plug module 130 comprises a metal plug 132 and a barrierlayer 134. The metal plug 132 is vertically disposed over the firstsource/drain 314. The barrier layer 134 surrounds the metal plug 132 andis electrically connected with the transition metal oxide layer 110. Inthe formation process of the non-volatile memory device 300, thetransition metal oxide layer 110 is made by reacting a portion of thedielectric layer 150 being directly below the metal plug 132 and aportion of the barrier layer 134 touching the portion of the dielectriclayer, and thereby a remaining portion of the dielectric layer 150remains on the first source/drain 314 after the transition metal oxidelayer 110 is formed.

It should be noted that the entire dielectric layer 150 is illustratedon the first source/drain 314 for illustrative purposes only; forexample, the dielectric layer 150 may be extended on the gate electrode312.

The transition metal oxide layer 110 is formed on the remaining portionof the dielectric layer 150, and the transition metal oxide layer 110 iselectrically coupled with the first source/drain 314 via the remainingportion of the dielectric layer 150.

It should be noted that the conductive plug module 130 is illustrated asa single one for illustrative purposes only; for example, a plurality ofconductive plug modules for multi-level memory may be disposed on thedifferent location areas of transition metal oxide layers, and the firstsource/drain 314 is disposed under the transition metal oxide layers.

In addition, a conductive plug (not shown) can be vertically disposed onthe second source/drain 316. For example, an external electricalpotential is applied to the second source/drain 316 through theconductive plug; alternatively, the external electrical potential isdirectly applied to the second source/drain 316. Please refer to FIG.2B. FIG. 2B is a cross-sectional view showing a non-volatile memorydevice 400 according to another embodiment of the present invention. Thenon-volatile memory device 400 is essentially the same as thenon-volatile memory device 300, except that the transition metal oxidelayer 110 is formed on the first source/drain 314, and thereby theremaining portion of the dielectric layer 150 surrounds the transitionmetal oxide layer 110. In the formation process of non-volatile memorydevice 400, the portion of the dielectric layer 150 between the metalplug 132 and the first source/drain 314 is combined with the portion ofthe barrier layer 134 to form the transition metal oxide layer 110contacting the first source/drain 314.

In practice, the non-volatile memory device 300 or 400 may utilize aresistance transition characteristic of the transition metal oxide 110wherein resistance varies according to a change in voltage. A pluralityof the non-volatile memory devices may constitute a resistance randomaccess memory (ReRAM).

In one case, ReRAM is structured as a metal-insulator-metal (MIM)structure, wherein a resistance-varying material is disposed between twometal layers. In above embodiment, it is different form the MIM ReRAM;the metal oxide layer 110 is formed between the metal plug 132 and thefirst source/drain 314.

Moreover, the method for operating the non-volatile memory device 300 or400 is disclosed as follows. When the non-volatile memory device 300 or400 is read, a first read voltage is applied between the gate electrode312 and the well 318 for turning on a channel between the firstsource/drain 314 and the second source/drain 316 in the well 318, and asecond read voltage is applied between the second source/drain 316 andthe metal plug 132 for generating electric current flowing through thechannel, the first source/drain 314 and the transition metal oxide layer110. For example, the channel is a n-channel, and the electricalpotential of the second source/drain 316 is greater than the electricalpotential of the metal plug 132 when the second read voltage is applied;alternatively, the channel is a p-channel, and the electrical potentialof the second source/drain 316 is less than the electrical potential ofthe metal plug 132 when the second read voltage is applied. Then, theamperage of the electric current is measured, and whether resistance ofthe transition metal oxide layer 110 is set or reset is decidedaccording to the amperage of the electric current with the predeterminedgate voltage. The predetermined gate voltage is designated forsufficient read current margin to differentiate set or reset state.

In the embodiment, when the nonvolatile memory device 300 or 400 is set,so that the resistance of the transition metal oxide layer 110 is turnedto be relatively low, and thereby the measured amperage of the electriccurrent is relatively high; on the contrary, when the non-volatilememory device 300 or 400 is processed with reset operation, so that theresistance of the transition metal oxide layer 110 is changed to berelatively high, and thereby the measured amperage of the electriccurrent is turned to be relatively low.

When setting the non-volatile memory device 300 or 400, a first setvoltage is applied between the gate electrode 312 and the well 318 forturning on the channel, and a second set voltage is applied between themetal plug 132 and the second source/drain 316 to set the resistance ofthe transition metal oxide layer 110. For example, the channel is an-channel, and the electrical potential of the second source/drain 316is greater than the electrical potential of the metal plug 132 when thesecond set voltage is applied; alternatively, the channel is ap-channel, and the electrical potential of the second source/drain 316is less than the electrical potential of the metal plug 132 when thesecond set voltage is applied. Thus, the resistance of the transitionmetal oxide layer 110 is relatively low.

When resetting the non-volatile memory device 300 or 400, a first resetvoltage is applied between the gate electrode 312 and the well 318 forturning on the channel after applying the first set voltage isperformed, and a second reset voltage is applied between the metal plug132 and the second source/drain 316 to reset the set resistance of thetransition metal oxide layer 110, wherein the absolute value of thesecond set voltage is greater than the absolute value of the secondreset voltage. For example, the channel is a n-channel, and theelectrical potential of the second source/drain 316 is less than theelectrical potential of the metal plug 132 when the second reset voltageis applied; alternatively, the channel is a p-channel, and theelectrical potential of the second source/drain 316 is greater than theelectrical potential of the metal plug 132 when the second reset voltageis applied. Thus, the resistance of the transition metal oxide layer 110is relatively high.

Please refer to FIG. 3. FIG. 3 is a graph depicting the state of then-channel non-volatile memory device of FIG. 2A. In the graph, theabscissa represents the voltage between the metal plug 132 and thesecond source/drain 316, and the ordinate represents the electriccurrent flowing through the transition metal oxide layer 110. A table ofthe state of the non-volatile memory device for each terminal is shownbelow:

Operation SET RESET Un- Un- READ Terminal Select select Select selectSelect Unselect gate electrode 0.8 V   0 V 2 V 0 V 1.2 V 0 V second 0 VFloat 0 V Float 0.4 V 0 V source/drain metal plug 4 V 0 V 1.8 V   0 V  0 V 0 V well (p-type) 0 V 0 V 0 V 0 V   0 V 0 V

When setting the n-channel non-volatile memory device, the first setvoltage that may be 0.8 V is applied between the gate electrode 312 andthe well 318, and the second set voltage that may be 4 V is appliedbetween the metal plug 132 and the second source/drain 316 to setresistance of the transition metal oxide layer 110; at this time, theelectric current flowing through the transition metal oxide layer 110 isabout 30 μA.

When resetting the n-channel non-volatile memory device the first resetvoltage that may be 2 V is applied between the gate electrode 312 andthe well 318; and the second reset voltage that may be 1.8 V is appliedbetween the metal plug 132 and the second source/drain 316 to reset theset resistance of the transition metal oxide layer 110.

When the n-channel non-volatile memory device is read, a first readvoltage that may be 1.2 V is applied between the gate electrode 312 andthe well 318, and a second read voltage that may be 0.4 V is appliedbetween the second source/drain 316 and the metal plug 132 forgenerating electric current flowing through the channel and thetransition metal oxide layer 110. Then, the amperage of the electriccurrent is measured, and whether the non-volatile memory device is setor reset is determined according to the amperage of the electric currentas shown in the graph.

Accordingly, the method for operating the non-volatile memory device canbe performed to alternately set/reset the resistance of the transitionmetal oxide layer 110, and the method may be repeated in an iterativemanner.

Please refer to FIG. 4A, FIG. 48 FIG. 4C and FIG. 4D. FIG. 4A, FIG. 48,FIG. 4C and FIG. 4D illustrate various process steps for manufacturing anon-volatile memory device having a transition metal oxide layeraccording to another embodiment of the present invention.

In FIG. 4A, a transistor is formed, where the transistor comprises agate electrode 312 and a first source/drain 314 and a secondsource/drain 316. In the formation process of the transistor, the gatedielectric layer 313 is disposed on a well 318, and the gate electrode312 is disposed on the gate dielectric layer 313, where the firstsource/drain 314 and the second source/drain 316 are formed at opposingsides of the gate electrode 312 in well 318. In addition, spacers 319are formed alongside the gate electrode 312.

Then, a dielectric layer 150 is formed on the first source/drain 314,where the dielectric layer 150 consists essentially of oxide material,wherein the oxide material is selected from the group consisting ofSiOx, SiOxNy and combinations thereof. In an alternative embodiment, thedielectric layer 150 is not only formed on the first source/drain 314but also is extended onto the gate electrode 312. Then, an interlayerinsulating layer 160 is formed on the dielectric layer 150 and thetransistor.

In FIG. 4B, at least one opening 162 through the interlayer insulatinglayer 160 to the dielectric layer 150 is formed by one or more etchingprocesses. In practice, some of the dielectric layer 150 is etchedaround the end of the opening 162, and thereby a defective texture of aportion 152 of the dielectric layer 150 is formed in situ.

In FIG. 4C, a barrier layer 134 is formed on an inner wall of theopening 162 and on the portion 152 of the dielectric layer 150 forreacting a portion of the barrier layer 134 with the portion 152 of thedielectric layer 150 contacting the portion of the barrier layer 134 toform a transition metal oxide layer 110, as shown in FIG. 4D. Thebarrier layer 134 may be titanium nitride, tantalum nitride andcombinations thereof; for example, the barrier layer 134 comprises oneor more layers of titanium nitride, tantalum nitride, or the like.

For instance, the barrier layer 134 contains titanium nitride, and thedielectric layer 150 contains silicon dioxide, so that the transitionmetal oxide layer 110 containing titanium oxide (TiOx) or titaniumoxynitride (TiON) is made by reacting titanium nitride with silicondioxide. Additionally or alternatively, the barrier layer 134 containstitanium nitride, and the dielectric layer 150 contains siliconoxynitride, so that the transition metal oxide layer 110 containingtitanium oxide (TiOx) or titanium oxynitride (TION) is made by reactingtitanium nitride with silicon oxynitride.

In the embodiment, the reacting procedure is performed at a temperatureabout 300° C.˜500° C. during manufacturing processes, alternatively,high-current flows through the barrier layer 134 and the dielectriclayer 150 for generating very high temperature locally (this is due tocontact plug area is usually very small, and a high current flowing thisregion will lead to a very high temperature at the local area), so as toform the transition metal oxide layer 110 by reacting a portion of adielectric layer 150 with a portion of the barrier layer; for example,during above set operation, the high-current flows through the barrierlayer 134 and the dielectric layer 150 for generating high temperaturelocally.

In FIG. 4D, a remaining portion of the dielectric layer 150 remains onthe first source/drain after the transition metal oxide layer 110 isformed, and a metal plug 132 is formed in the opening 162 forelectrically connecting the metal plug 132 with the transition metaloxide layer 110 after the barrier layer 134 is formed.

In FIG. 4C and FIG. 4D, the process step of forming the barrier layer134 on the dielectric layer 150 is performed to form the transitionmetal oxide layer 110 on the remaining portion of the dielectric layer150. In an alternative embodiment, the process step of forming thebarrier layer 134 on the dielectric layer 150 is performed to form thetransition metal oxide layer on the first source/drain 314 as shown inFIG. 2B, and thereby the remaining portion of the dielectric layer 150surrounds the transition metal oxide layer 110.

For an integrated information, the multi-layers (132/110/150/314) inFIG. 4 may be the stacked structure, e.g., W-plug/TiN/TiON/SiO2/Si fromtop to bottom. the multi-layers (132/110/314) in FIG. 2B may be thestacked structure, e.g., W-plug/TiN/TiON/Si from top to bottom. Inalternative embodiment, the multi-layers (132/110/150/314) in FIG. 4 maybe the stacked structure, e.g., W-plug/TiN/TiOx/SiO2/Si from top tobottom the multi-layers (132/110/314) in FIG. 2B may be the stackedstructure, e.g., W-plug/TiN/TiOx/Si from top to bottom.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentinvention Those skilled in the art should appreciate that they mayreadily use the present invention as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentinvention, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent invention.

1. A variable and reversible resistive element, comprising: a transitionmetal oxide layer for resistance change; a bottom electrode disposedunder the transition metal oxide layer; and at least one conductive plugmodule disposed on the transition metal oxide layer, comprising: a metalplug vertically disposed over the bottom electrode; and a barrier layersurrounding the metal plug and electrically connected with thetransition metal oxide layer, wherein the transition metal oxide layeris made by reacting a portion of a dielectric layer being directly belowthe metal plug with a portion of the barrier layer touching the portionof the dielectric layer, wherein the dielectric layer is formed on thebottom electrode, and thereby a remaining portion of the dielectriclayer remains on the bottom electrode after the transition metal oxidelayer is formed.
 2. The variable and reversible resistive element ofclaim 1, wherein the transition metal oxide layer is formed on theremaining portion of the dielectric layer, and the transition metaloxide layer is electrically coupled with the bottom electrode via theremaining portion of the dielectric layer.
 3. The variable andreversible resistive element of claim 1, wherein the transition metaloxide layer is formed on the bottom electrode, and thereby the remainingportion of the dielectric layer surrounds transition metal oxide layer.4. The variable and reversible resistive element of claim 1, wherein thedielectric layer consists essentially of oxide material.
 5. The variableand reversible resistive element of claim 4, wherein the oxide materialis selected from the group consisting of SiOx, SiOxNy, SixNy andcombinations thereof.
 6. The variable and reversible resistive elementof claim 1, wherein the barrier layer comprises barrier material,wherein the barrier material is selected from the group consisting oftitanium nitride, tantalum nitride and combinations thereof.
 7. Thevariable and reversible resistive element of claim 5, wherein the metalplug comprises metal, wherein the metal is selected from the groupconsisting of tungsten, nickel, copper, aluminum and combinationsthereof.
 8. The variable and reversible resistive element of claim 1,wherein the bottom electrode consists essentially of an impurity-dopedregion within or upon a semiconductor substrate.
 9. A method foroperating the non-volatile memory device of claim 8, comprising:applying a first read voltage between the gate electrode and the wellfor turning on a channel between the first source/drain and the secondsource/drain in the well; applying a second read voltage between thesecond source/drain and the metal plug for generating electric currentflowing through the channel and the transition metal oxide layer;measuring amperage of the electric current; and deciding whetherresistance of the transition metal oxide layer is set or reset accordingto the amperage of the electric current.
 10. The method of claim 9,further comprising: applying a first set voltage between the gateelectrode and the well for turning on the channel; and applying a secondset voltage between the metal plug and the second source/drain to setthe resistance of the transition metal oxide layer.
 11. The method ofclaim 10, further comprising: applying a first reset voltage between thegate electrode and the well for turning on the channel after applyingthe first set voltage is performed; and applying a second reset voltagebetween the metal plug and the second source/drain to reset the setresistance of the transition metal oxide layer, wherein the absolutevalue of the second set voltage is greater than the absolute value ofthe second reset voltage.
 12. The method of claim 9, wherein the channelis a n-channel, and the electrical potential of the second source/drainis greater than the electrical potential of the metal plug when thesecond read voltage is applied.